In the field of MEMS devices it is advantageous to be able to permanently change the positions of structures manufactured in planar technology. This may be exploited, for example, for component properties such as resonant frequency. In addition, this may be also be utilized for the defined positioning of structures in three-dimensional space, for example for mirrors or electrodes.
There are various known possibilities of achieving the angle/lift offset relative to the planar surface of the layer or substrate, which is necessary for the deflection, said layer or substrate having an MEMS device realized therein.
A first approach is to utilize the bimorph effect. Here, the structures employed have applied thereon, by applying a layer, an intrinsic stress resulting in an angle, or to a difference, between a flat surface, normally the surface of the layer, and the actuator formed in the layer, that is the MEMS device. This procedure results in layer stresses, which in turn result in the structures being “positioned” relative to the layer surface. The disadvantage of this procedure is that here the actuators are automatically activated once they have been exposed.
A further approach known is to exploit surface forces for positioning an actuator. The structures used here have a mechanical stress applied to them by applying a liquid, for example a polymer, said mechanical stress in turn resulting in an angle or a difference between the flat surface and the actuator. Unlike the bimorph effect described above, wherein the structures where positioned on the basis of layer stresses, positioning of the structures here is achieved on the basis of the surface tensions of the polymer used. The disadvantage of this procedure is that a very high level of dosage accuracy is necessary for applying the liquid so as to be able to achieve specific repeatability of the surface states. This approach of using surface forces is employed, for example, by Patterson, P. R. et al. in “A Scanning Micromirror With Angular Comb Drive Actuation”, pages 544-547, Micro Electro Mechanical Systems, IEEE Las Vegas, 2002.
A further approach known to positioning the actuators consists in using mechanical elements. The structures used here are positioned below or above the flat surface by a mechanical element, possibly temporarily using thermal fixation in the position. This is effected, for example, within the framework of the manufacturing steps for finishing the devices which follow the production of the MEMS devices, for example within the framework of structural design and coupling technology. The disadvantage of this procedure is that a very high level of positioning accuracy, or tight tolerances, are necessary. This approach is described, for example, by Jongbaeg Kim, et al. in “Microfabricated Torsional Actuators Using Self-Aligned Plastic Deformation of Silicon”, Journal of Microelectromechanical Systems, VOL. 15, NO. 3, June 2006.
In addition, one has known an approach using so-called multilayers. Here, a layer stack of several conductive layers which are insulated from one another is provided which enables three-dimensional potential distribution. This approach is only possible with expensive process steps, necessitates expensive contacting, and results in only small deflections. This approach is described, for example, by Huikai Xie, et al. in “Vertical Comb-finger Capacitive Actuation And Sensing For CMOS-MEMS”, IEEE International Workshop on Micro Electro Mechanical Systems (MEMS—2001) No. 14, Interlaken, 2002, vol. 95, no. 2-3 (20 ref.), pages 212-221.
Yet another approach known is to use different layer thicknesses. Here, different geometrical dimensions of an actuator and a counter electrode are selected to enable a deflection of the element. The disadvantage of this procedure is that only small deflections are possible, as is described by W. Noell, et al. in “Compact And Stress released Piston Tip tilt Mirror” SPIE 6186-16, 2006.
The above brief discussion shows that one has known various approaches of deflecting an MEMS device, for example an actuator, and positioning it in the deflected position. However, the known approaches have a number of disadvantages associated with them, namely that the elements which cause the deflection and positioning of the MEMS structures have intrinsically had this property and therefore do not enable activation at any predefined point in time. Rather, the activation is specified by the progress made in the process during manufacturing of the overall structure. A further disadvantage is that the conventional approaches have only a low level of positioning accuracy and a low level of repeatability. In addition, the known approaches place very high demands upon the alignment accuracy.